1. Field of the Invention
The present invention relates to a driving unit for an image forming apparatus, a color image forming apparatus having the same, and a method of manufacturing an image forming apparatus having the driving unit.
2. Description of the Related Art
Generally, image forming apparatuses are classified into a monochromatic image forming apparatus and a color image forming apparatus. The monochromatic image forming apparatus forms an image in black and white by using only one color developer, while the color image forming apparatus forms a colorful image by using color developers such as magenta, cyan, yellow, and black.
An electrophotographic image forming apparatus forms an electrostatic latent image by scanning a laser beam onto an organic photoconductor (OPC), which is electrified by an electrifying unit to have a predetermined level of electric potential, using a light exposing unit. The electrostatic latent image is developed using a developer and then transferred into a visible image on supplied print paper. In a color image forming apparatus, the electrostatic latent image is developed by using color developers on the organic photoconductors and overlapped images are transferred onto an intermediate transfer medium, such as an Intermediate Transfer Belt (ITB). The color images overlapped on the intermediate transfer medium are transferred onto print paper. Subsequently, the print paper with a color image goes through a series of fixing processes before it is transferred out of the image forming apparatus.
FIG. 1 is a structural diagram showing a conventional color image forming apparatus that performs a two-step transferring process by using the intermediate transfer medium. Referring to FIG. 1, the color image forming apparatus comprises a belt 10, a supporting roller 11, four T1 rollers 12, 13, 14 and 15, four organic photoconductors 16, 17, 18 and 19, a T2 roller 20, and a belt driving roller 21.
Developers each corresponding to K (black), C (cyan), M (magenta), and Y (yellow) are attached to the electrostatic latent image area of each of the organic photoconductors 16, 17, 18 and 19. The T1 rollers 12, 13, 14 and 15 are set up to correspond to the organic photoconductors 16, 17, 18 and 19 with the belt 10 between the organic photoconductors 16, 17, 18 and 19 and the T1 rollers 12, 13, 14 and 15. Accordingly, the developers attached to the surfaces of the organic photoconductor 16, 17, 18 and 19 are primarily transferred to the surface of the belt 10 by the transferring activity of the T1 rollers 12, 13, 14 and 15. Herein, the respective color images of the organic photoconductors 16, 17, 18 and 19 are transferred onto the belt 10 at predetermined time intervals so that the color developers transferred to the belt 10 can be overlapped in registration into a complete color image. Therefore, the color developers are overlapped on the belt 10 to thereby form a complete color image. Subsequently, the color image on the belt 10 goes through a secondary transferring process between the T2 roller 20 and the belt driving roller 21. Also, the belt driving roller 21 runs the belt 10 at a proper rate.
The belt 10 and the organic photoconductors 16, 17, 18 and 19 are consumption goods with limited life spans, that must periodically be replaced.
A transferring unit including the belt 10 and developing units including each organic photoconductor 16, 17, 18 or 19 are typically set up in a detachable manner along with a predetermined coupling unit and the driving unit for providing power in the image forming apparatus.
When the consumption goods, that is, the transferring unit and the developing units, are replaced, the structure of the coupling unit for performing relative motion of the driving unit, the transferring unit, and the developing units is significant. That is, it is important to connect the transferring unit and the developing units to have the same rotational axis as the driving unit. It is also important to realize highly precise color registration in consideration of the so-called total runout between the transferring unit and the developing unit. This is particularly important in view of manufacturing tolerances in the external circumferential surface of the driving roller of the transferring unit.
Herein, the total runout can be understood to include a phenomenon that the belt 10 rotates at a predetermined rate, but small changes in the instantaneous rotation rate occur due to the manufacturing tolerance of the external circumferential surface of the driving roller. The total runout affects the developing units in the same period through the belt 10. Therefore, it is important to equalize the influence of the total runout on the developing units and improve the quality of a color image.
Additionally, the organic photoconductors and the driving roller may have deviations in their radii if the outer circumferences thereof do not make a perfect circle due to manufacturing tolerances. Such deviations result in errors of a composite color image on the belt as the color image partially stretches or cuts due to the aforementioned deviations in the OPC rollers and the driving roller.